The present invention is generally related to drive circuits for electromechanical machines, and, more particularly, the present invention is related to an improved drive circuit topology that uses a split winding for driving a switched reluctance machine.
FIG. 1 shows a standard drive circuit topology 10 generally used to drive a switched reluctance machine and referred in the art as asymmetric bridge. FIG. 1 shows the drive circuit topology as applied to a single phase of a polyphase switched reluctance machine and, as shown in FIG. 1, such circuit topology includes two power switches and two power diodes per motor phase. As will be readily understood by those skilled in the art, power is supplied to a motor phase winding 12 from a direct current (DC) source, such as a battery (not shown). A capacitor 11 is connected across first and second supply links 14 and 16. Winding 12 is connected across links 14 and 16 by upper and lower switches 17 and 18. Diodes 20 and 22, generally referred to in the art as xe2x80x9cfree-wheelingxe2x80x9d diodes, circulate inductive current in the phase winding when one or both of the respective switches are turned off. In operation, phase winding 12 is energized by turning on switches 17 and 18. Current in the phase winding may be regulated, based on a suitable regulation technique, such as pulse-width-modulation (PWM), by sending the PWM signals to either of switches 17 or 18. Winding current during off periods of the PWM may be re-circulated through the conductive switch and one of the free-wheeling diodes 20 or 22. This is called zero voltage loop. When both upper and lower switches 17 and 18 are turned off to terminate the energization interval, both free-wheeling diodes 20 and 22 may conduct to return winding current to the DC source.
One issue with drive circuit 10 is that if higher power is required for a given machine, the power rating of each silicon-based power device needs to be increased proportionally. This may force the designer to use higher-power-rated devices to account for worst-case scenarios and generally results in higher costs. In view of the foregoing, it would be desirable to provide an improved drive circuit topology that is able to boost torque for a motoring mode or generated current for a generating mode without increase of the power rating of the power devices. This would result in more efficient use of the silicon-based devices, and would lower costs of the drive circuit.
Generally speaking, the present invention fulfills the foregoing needs by providing in one aspect thereof a drive circuit for a switched reluctance machine having at least two windings per pole. The circuit includes first and second direct current links. The circuit further includes a first winding having first and second terminals. The first winding is connectable across said first and second links. A first switch is coupled across the first link and the first terminal of the first winding. A second switch is coupled across the second terminal of the first winding and the second link. A second winding is connectable in series circuit to that first winding. The second winding has first and second terminals. A third switch is coupled across one of the first and second links and the second terminal of the second winding. Each of the switches is responsive to a respective gating signal to selectively energize and deenergize one of the windings when the machine operates in a first mode of operation and to selectively energize and deenergize both of said windings when the machine operates in a second mode of operation.
The present invention further fulfills the foregoing needs by providing a method for driving a switched reluctance machine having at least two windings per pole. The method allows for providing first and second direct current links. The method further allows for providing a first winding having first and second terminals. The first winding is connectable across said first and second links. A first switch is coupled across the first link and the first terminal of said first winding. A second switch is coupled across the second terminal of said first winding and the second link. The method further allows for providing a second winding connectable in series circuit to the first winding. The second winding has first and second terminals. A third switch is coupled across one of the first and second links and the second terminal of said second winding. Each of the switches is responsive to a respective gating signal to selectively energize and deenergize one of the windings when the machine operates in a first mode of operation and to selectively energize and deenergize both windings when the machine operates in a second mode of operation.